Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	$ 142	$ 152
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	104	112
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	529	136
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	510	138
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	621	440
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	546	377
DB SERP
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	10	10
Non-current liabilities	139	150
DB SERP | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	7	7
Non-current liabilities	$ 102	$ 110